The present invention relates to a grommet with a closed airspace inside thereof providing enhanced sound insulation.
Japanese Unexamined Patent Publication No. 9(1997)xe2x80x94289723 discloses a grommet including an outer tubular portion, an inner tubular portion, a shield wall interconnecting the outer and inner tubular portions, a sound insulation wall on the inner tubular portion and an engaging member on the outer tubular portion.
In this grommet, the engaging member and the sound insulation wall must be rigid to a certain degree, since the sound insulation wall needs to maintain engagement with the engaging member remaining inside the outer tubular portion even when the inner tubular portion is inclined with respect to the outer tubular portion. Therefore, a large force is necessary to get the sound insulation wall to go over the engaging member and to enter into the outer tubular portion, making the insertion of the sound insulation wall into the outer tubular portion very hard.
The engaging member or the sound insulation wall can be of reduced rigidity in order to facilitate insertion, however, the sound insulation wall easily disengages from the engaging member in this case, the hermetical seal of an airspace closed by the engagement is lost, and a sound insulation can not be maintained.
The object of the present invention is to provide a grommet with a sound insulation wall insertable into an outer tubular portion with small insertion force, in which the inserted sound insulation wall is not easily releasable, thereby maintaining reliable sound insulation.
A first aspect of the present invention is a grommet comprising: a first tubular portion holding an electric wire therein; an elastic first flange formed on a front part of the first tubular portion; a second tubular portion extending rearward from the first flange, the second tubular portion to be fitted in a panel hole as the first tubular portion is pulled frontward, the second tubular portion cooperating with the first tubular portion and the first flange to define an annular space; a rib portion annularly formed on the second tubular portion, defining an entrance to the annular space; and an elastic second flange formed on a rear part of the first tubular portion, diverging rearward to extend in a radial direction outside the entrance of the annular space, wherein, as the first tubular portion is pulled frontward to fit the second tubular portion in the panel hole, the first flange elastically deforms to allow the first tubular portion to move frontward relative to the second tubular portion, the second flange deforms and goes over the rib portion to enter the annular space, and, as the first tubular portion is released, the second flange, in an inverted shape diverging frontward, engages with the rib portion and closes the annular space.
Preferably, the rib portion is divided into a plurality of ribs by a cut in a radial direction of the second tubular portion.
According to the first aspect of the present invention constituted as described above, by pulling the electric wire held by the first tubular portion frontward, the second tubular portion extending rearward from the first flange is fitted in the panel hole. Here, the first flange elastically deforms in an axial direction in a manner whereby an inner periphery thereof is pulled by the first tubular portion, to allow the first tubular portion to move frontward relative to the second tubular portion. The second flange formed on the rear part of the first tubular portion elastically deforms and goes over the annular rib portion formed on the second tubular portion, and enters the annular space inside the second tubular portion.
Since the second flange is diverging rearward, the second flange can easily enter the annular space inside the second tubular portion with little force, even though the second flange extends in a radial direction outside the entrance of the annular space. In addition, if the annular rib portion to engage with the second flange is divided into a plurality of ribs, it can be further flexible. Owing to the flexure of the both members, the second flange can easily get over the rib portion and enter the annular space inside the second tubular portion with little force.
After the second flange enters the annular space and the second tubular portion is fitted into the panel hole, when the electric wire is released, the first tubular portion is restituted to an initial position owing to the resilience of the first wall. An outer periphery of the second flange engages with the rib portion on the second tubular portion, the second flange is inverted pivoting on the outer periphery thereof to be in the inverted shape diverging frontward, and the annular space is closed. In this state, the outer periphery of the second flange firmly contacts with the rib portion with resilience of the second flange to recover its initial shape, whereby hermetic sealing is maintained. Moreover, the closed annular space functions as a sound barrier of airspace between the inside and the outside of the panel, thus enhancing the sound insulation of the grommet.
Since the second flange is diverging rearward, once the outer periphery of the second flange gets over the rib portion and engages therewith, the outer periphery of the second flange tends to deform in a manner that a biting margin (an engaging margin) of the second flange overlapping the rib portion becomes larger when the first tubular portion is displaced rearward relative to the second tubular portion. Moreover, since both the second flange and the rib portion are made flexible, the engagement thereby is not released. Hence, the airspace is reliably maintained, whereby high sound insulation can be secured.
Whereas the second flange and the rib portion are flexible, engagement therebetween is not easily releasable. Even when lateral force is applied to the electric wire and the first tubular portion is inclined relative to the second tubular portion, the state of engagement between the rib portion and the second flange and the hermetic sealing of the closed annular space is maintained. Such an aspect is attributable to a synergy of a conical shape of the second flange and flexibilities of both of the second flange and the rib portion.
A second aspect of the present invention is the grommet according to the first aspect, in which the first flange is in a conical shape, as an initial shape thereof, diverging frontward.
Preferably, the first flange can be in an inverted shape diverging rearward, allowing the first tubular portion to move frontward relative to the second tubular portion.
Further preferably, the second flange can be in the inverted shape diverging frontward and engage with the rib portion owing to resilience of the first flange in the inverted shape diverging rearward to recover the initial shape.
According to the second aspect of the present invention constituted as described above, since the first flange has the initial shape of the conical shape diverging frontward, resilience thereof in the inverted shape diverging rearward to recover the initial shape generates a force strong enough to move the first tubular portion to an original position relative to the second tubular portion and to invert the second flange into the inverted shape diverging frontward. Accordingly, the attachment of the grommet to the panel is completed simply by pulling and releasing the electric wire.